Electrodeposition of bright zinc



Patented Jan. 29, 1946 2,393,741 ICE ELECTRODEPOSITION OF BRIGHT ZINC John Leighton Bray, La Fayette, and Robert. Eugene Howard, West Lafayette, Ind., assignors to Purdue Research Foundation, La Fayette, Ind., a corporation of Indiana No Drawing. Original application October 3,

1941, Serial No. 413,502. 'Divided and this application September 30, 1943, Serial No. 504,434

1 Claim.

This invention relates generally to the electrodeposition of zinc, and paritcularly to a process and materials by means of which bright, continuous deposits of zinc may be obtained electrolytically from acid zinc sulfate solutions.

The present application is a division of our application Serial No. 413,502, filed October 3, 1941, for Eiectrodeposition of bright zinc.

In the past, most of the methods used in electrogalvanizing resulted in dark or dull plates which had neither eye-appeal nor too great utility as protective coatings because of the coarseness and non-uniformity of the deposit on the plated objects.

Heretofore the electroplating of zinc from suli'ate solutions was carried on almost universally at rather low current densities, usually of the order 01' amperes per square foot. Much higher current densities, approximatin 1000 amperes per square foot,- have'been employed recently in the electrodeposition of zinc; however, this Work has been directed exclusively to the electro-winning of zinc from its ores.

We have discovered that bright zinc may be.

deposited electrolytically, between certain limits of current density, from acid zincsulfate solutions which contain triethylene tetramine as an addition agent. In order tov acquaint those skilled in the art with the nature of our addition product and the range of current density within around the periphery of the cathode, provision was made for rotating it at between substantially 15 and 20 revolutions per minute. The test samples were plated until a deposit corresponding to the commercial designation'of about two ounces per square foot was obtained. 7

The cathodes were cleaned by subjecting them to an anodic pickling treatment in a 10% suifuric acid solution for one minute at a current density of approximately 600 amperes per square foot.

' The anodes employed in our experiments were pure lead and had-an area of approximately eleven times that of the cathode, thus making the anode current density correspondingly small than that of the cathode.

The variables of temperature, acidity, and concentration of zinc sulfate were kept practically constant. It was discovered that predictable results could be obtained when the temperature of the plating solution was maintained between 14 C. and 20" C., the acidity at approximately 0.5 N, and the concentration of zinc sulfate be tween 20% and 24%. Unde these conditions the effect of current density and concentration of the addition agent was investigated. v

A series of solutions were prepared in which the concentration of the addition agent varied from 0.11 M to 0.15 M. Each solution was treated electrolytically at a number of current densities and the appearance ,of the plated object (cathode) observed. The luster characteristic of each sample was classified according to its reflectivity: matte, meaning a dull finish, showing no luster whatever; semi metallic refer-- ring to the borderline case between matte and metallic luster; metallic" referring to a good reflective deposit; and mirror denoting only the most highly reflective deposits. Whenever 40 the term bright is used in this application to which a satisfactory bright zinc deposit may be I obtained, we will now set out the findings of 'our experiments and illustrate. our process by several specific examples.

In the procedure followed in our investigations it was found desirable to maintain constant all known variables except the one under consideration.- Accordingly, solutions of known concentrations in zinc sulfate, sulfuric acid, and the addition agent were subjected to electrolysis at different current densities. The cathodes em-- ployed were low-carbon, bright-annealed, steel wires, 0.106 inch in diameter and approximately seven inches long. Four inches of this length describe the luster characteristic of the zinc deposit, it i intended to include all the degrees of luster covered by the terms semi-metallic, metallic, and mirror.

The efiect of triethylene tetramine as an addition agent is shown in the following tables:

Table I.Operating data and observation of samples plated at 0.11 M triethylene tetramine Av. solu Current den- Time s1ty,amperes gg of run, Color luster per sq. ft. min.

600 18 5 Lt. grey matte. 200 18 .10 Dk. grey met.

150 17 10 Do. 15 15 Do. 300 15 1O Lt. grey met. 400 16 8 Lt. grey semi-met. 250 15 12 Lt. grey met. 270 15 10 Do. 1, 000 18 3 Lt. grey matte.

.Dk. grey met.

Table lL-sampl es plated at 0.13 M triethylene tetramine Av solu- Current den- Time Sample tier: sity, amperes of run, Color luster number per sq. it. i a min.

601..... 600 17 5 Dk. grey semi-met. 002..... 200 17 Lt. grey met. G03..." 300 16 10 Lt. grey semi-met. 10 GC4 250 12 Do. G05"-.. 15 15 Dk. grey met. GC6. 150 16 12 D0. 607..... 200 15 11 Lt. grey met. 008..... 300 15 7 Do. 609..... 400 16 7 Lt. grey semi-met. 0010--.. 500 17 7 Do. GC 1,000 20 3 D0. 15

Table [IL-Samples plated at 0.15 M methylene tetramine Av. solu- 20 Current den- Time Sample tion sity, amperes or run, Color luster number per sq. it. a min. I

GB1- 600 18 8 Dk. grey matte. 6132..." 200 18 10 Do. 0133..... 1; 000 20 3 Do.

B4....- 2, 000 22 1% Lt. grey matte. G"--- 100 18 15 DX. grey met. GB6--... 50 15 15 Dk. grey semi-met. GB7 14 10 Lt. grey mirror. G B8 14 8 Do. G B9 200 15 15 Do. G 810-... 300 16. 10 Do. 0.811.-.. 400 16 7 Lt. greymet. 67812.... 500 17 6 Lt.- grey semi-met. G 313---- 50 17 15 Dk. grey met. G 314... 600 16 5 Lt. grey semi-met. G 315--.. 250 '16 10" Lt. grey met. G 316.... 200 16 l0 Lt. grey mirror. G 817.... 200 16 10 ;Do.

It will thus be obseryed that bright zinc de-' posits may be obtained from acid zinc sulfate solutions "by using triethylene tetramine as an addition agent at concentrations of about 0.15 M

and current densities between 150 and 600 amperes per square foot. 1

Having described our invention, what we claim and wish to protect byLetters Patent is:

The process of producing bright electro-deposited zinc which comprises plating zinc onto a cathode at a current density in the range from acid, said addition agent being triethylene tetramine and being present in the vbath in quantity to provide a molar concentration of about JOHN LEIGHTON BRAY. ROBERT EUGENE HOWARD. 

